1. Field of the Invention
The invention concerns the stabilization of the attitude of a satellite (or, more generally, a spacecraft station carrying a payload) in terrestrial orbit, in practice a circular orbit and preferably a geostationary orbit.
2. Description of the Prior Art
At present three-axis stabilized geostationary satellites are almost exclusively all telecommunication satellites for which pointing in yaw and stability with regard to high-frequency vibration are not critical criteria.
Such satellites in practice carry momentum wheels conferring upon them sufficient gyroscopic stiffness to reduce yaw errors (this applies in particular to the ARABSAT, EUTELSAT-2 and TVSAT-2 satellites).
This attitude control principle is insufficiently accurate for meteorological remote sensing satellites for which the accuracy of the attitude of the satellite is a critical parameter; similar precision is also a requirement, to which no more satisfactory a solution has yet been found, in the case of scientific experiment spacecraft, for example.
Broadly speaking, the first criterion which must be satisfied by a telecommunication satellite is that it should be cost-effective, and therefore of low cost, whereas remote sensing and "scientific experiment" satellites must meet performance criteria irrespective of the cost implications.
The previously mentioned solution using momentum wheels for stabilization has drawbacks including a high level of vibration even though the passive gyroscopic yaw control that it provides is necessarily imprecise.
The invention is directed to enabling highly accurate attitude control of a three-axis stabilized geostationary satellite or spacecraft of the active control type, but offering high reliability; minimizing use of thrusters and so improving the stability of the spacecraft; minimizing transient orbit control conditions; facilitating seasonal 180.degree. slew maneuvers; enabling compensation of internal disturbances on these three axes; and minimizing the problems of onboard resonance.